In the student assessment industry, virtually perfect capture recognition of marks is desirable. Several factors mitigate against perfection in this endeavor, including imperfect print quality, imaging distortions, damage to forms in the field, etc.
A common approach to processing forms involves the use of special inks and lighting that causes the pre-printed marks on the page to drop out, leaving only reference marks or timing tracks in a visible ink, along with pencil marks on the page. This approach relies solely on the location of marks on the page relative to the edge of the page, the reference marks or the timing tracks to locate the invisibly captured “bubbles” in which marks may appear. Graphite from a mark in the selected bubble remains visible, and is captured and processed.
Drop-out technologies tend not to provide any indication when damaged, misprinted, crumpled, or otherwise anomalous pages are captured, as long as the reference marks remain in place. For example, imperfections may be introduced by small variations in the speed of travel of the page under the scanner.